Conventionally, a configuration is employed which variably controls direct-current (DC) voltage which is to be input to an inverter for performing DC-to-AC voltage conversion. For example, Japanese Patent Laying-Open No. 2010-166719 (PTL 1) discloses a motor drive control device for driving a compressor for an air conditioner, the motor drive control device having a configuration in which a boost converter is disposed between a DC power supply, configured of a three-phase alternating-current (AC) power supply and a three-phase rectifier circuit, and an inverter for supplying AC voltage to a motor.
Use of the boost converter can increase a DC voltage, which is to be input to the inverter, above an input voltage from the DC power supply. With this, the motor can be appropriately driven in a high rotational speed range where an induced voltage is increased, while avoiding an increased loss or a temperature increase due to an increase of the motor current.
WO2016/002053 (PTL 2) discloses a power conversion device having a configuration in which a multi-level chopper circuit is connected between a DC power supply and an inverter which are similar to PTL 1. The boost modes of the multi-level chopper circuit are switchable according to loading condition of an AC motor, thereby reducing the cost by size reduction of switching elements, and improving the operating range of the AC motor owing to an increase in step-up ratio.